1. Field of the Invention
The present invention relates to an imaging lens that is used in a vehicular camera, a cell phone camera, a surveillance camera, or the like having an imaging device such as a CCD (charge-coupled device) sensor or a CMOS (complementary metal oxide semiconductor) sensor. And the invention mainly relates to, for example, a wide-angle imaging lens that is used in a vehicular camera for taking an image of a front sight, a side sight, a rear sight, or the like as viewed from a vehicle.
2. Description of Related Art
In recent years, imaging devices such as CCD sensors and CMOS sensors have been increased greatly in miniaturization and the number of pixels. Accordingly, imaging apparatus main bodies and lenses mounted thereon are required to be reduced in size and weight. On the other hand, a wide-angle lens having a large angle of view (e.g., 140° or more diagonally) is required in vehicular cameras etc.
Among wide-angle imaging lenses having a relatively small number of lenses are ones disclosed in JP-A-7-72382, JP-A-2001-337268 and JP-A-2002-244031. JP-A-7-72382 discloses a wide-angle lens for a CCD camera which has a three-lens configuration. JP-A-2001-337268 discloses a wide-angle lens including three aspherical lenses. JP-A-2002-244031 discloses a wide-angle lens including a total of four lenses which are divided into a first group and a second group.
However, the wide-angle lens of JP-A-7-72382 is not sufficient in miniaturization and angle-of-view increase. The wide-angle lens of JP-A-2001-337268 employs a plastic aspherical lens as the first lens. However, in such cameras as vehicular cameras which may be used in an environment in which high weather resistance is required, it is preferable that the first lens be made of glass. In the wide-angle lens of JP-A-2001-337268, since the first lens is an aspherical lens, forming the first lens with glass is costly. The wide-angle lens of JP-A-2002-244031, which consists of four lenses, is disadvantageous in cost and weight reduction though it is advantageous in performance.